fix: 修复天象事件 API 在事件边界附近的重复返回问题

- 修正合月、合日、留等Last/Next/Closest接口在精确命中和事件后秒级查询时仍返回当前事件的问题，避免应用侧枚举卡死
- 收紧事件边界判定，并补强水星、金星、火星近事件路径的稳定化，保证公开API的单调前进语义
- 补充公开wrapper、跨世纪样本和外部基线回归，覆盖合月邻近事件与边界场景

basic/inner_event_window.go

@@ -2,7 +2,11 @@ package basic
 
 import "math"
 
-const innerEventEpsilon = 4.0 / 86400.0
+const (
+	innerEventEpsilon         = 0.1 / 86400.0
+	innerEventWindowPadding   = 4.0 / 86400.0
+	innerEventMaximizeEpsilon = 4.0 / 86400.0
+)
 
 func eventQueryTTAsUT(queryTT float64) float64 {
 	return TD2UT(queryTT, false)
@@ -157,7 +161,7 @@ func maximizeInWindow(start, end, coarseStep float64, coarseFn, exactFn func(flo
 	guess := scanWindowForMax(start, end, coarseStep, coarseFn)
 	left := clampFloat64(guess-coarseStep, start, end)
 	right := clampFloat64(guess+coarseStep, start, end)
-	if right-left <= innerEventEpsilon {
+	if right-left <= innerEventMaximizeEpsilon {
 		return guess
 	}
 	for i := 0; i < 20; i++ {